1. Field of Invention
This invention relates to electrostatographic imaging devices.
2. Description of Related Art
Electrostatic reproduction involves uniformly charging a photoconductive member, or photoreceptor, and imagewise discharging it, or imagewise exposing it, based on light reflected from an original image being reproduced. The result is an electrostatically-formed latent image on the photoconductive member. The latent image is developed by bringing a charged developer material into contact with the photoconductive member.
Two-component and single-component developer materials are known. Two-component developer materials comprise magnetic carrier particles and charged toner particles that adhere triboelectrically to the carrier particles and are intended to adhere the photoconductive member.
A single-component developer material typically consists of only toner particles. The toner particles typically have an electrostatic charge to adhere to the photoconductive member, and magnetic properties to magnetically convey the toner particles from the sump to the magnetic roll. The toner particles adhere directly to the donor roll by electrostatic charges. The toner particles are attracted to the donor roll from a magnet or developer roll. From the donor roll, the toner is transferred to the photoconductive member in the development zone.
For both types of developer material, the charged toner particles are brought into contact with the latent image to form a toner image on the photoconductive member. The toner image is transferred to a receiver sheet, which passes through a fuser device where the toner particles are heated and permanently fused to the sheet, forming a hard copy of the original image.
A development device is used to bring the charged toner particles into contact with the latent image formed on the photoreceptor, so that the toner particles adhere electrostatically to the charged areas on the latent image. The development device typically includes a chamber in which the developer material is mixed and charged.
One type of two-component development method and apparatus is known as xe2x80x9cscavengeless development.xe2x80x9d In scavengeless development systems, toner is detached from the donor roll by applying an alternating current (AC) electric field to electrodes disposed between the donor roll and the photoconductive member. There is no physical contact between the development apparatus and the photoconductive member. Scavengeless development is useful in apparatus in which different types of toner are supplied to the same photoconductive member. xe2x80x9cHybridxe2x80x9d scavengeless development apparatus typically include a mixing chamber that holds a two-component developer material, a developer material developer or magnetic roll, a donor roll, a development zone, and an electrode structure at the development zone between the donor roll and the photoconductive member. The donor roll receives charged toner particles from the developer roll and transports the particles to the development zone. An AC voltage is applied to the electrodes to form a toner cloud in the development zone. Electrostatic fields generated by an adjacent latent image on the photoconductive member surface attract charged toner particles from the toner cloud to develop the latent image on the photoconductive member.
Another variation on scavengeless development uses single-component developer material development systems. As in two-component developer material development systems, the donor roll and electrodes also create a toner cloud.
In both one-component and two-component developer scavengeless development systems, the electrical, chemical and physical characteristics of the donor roll affect the ability of the development apparatus to effectively transport toner particles into the development zone and to achieve high-quality image development. The donor roll should have characteristics that enable charged toner particles to effectively and controllably adhere electrostatically to the donor roll""s outer surface. In addition, the donor roll should have the desired electrical properties for donating toner particles to the photoconductive member. It is desirable that the electrical properties of the donor roll be uniform and also be tunable.
It is also desirable that the outer surface of the donor roll have a smooth finish or low roughness.
It is also desirable that the outer surface of the donor roll have good machining characteristics so that a desired surface finish can be formed in less time and with reduced cost.
The donor roll outer surface should also have sufficient wear resistance to resist abrasion when contacted by other surfaces.
This invention provides rolls that have outer coatings with physical, electrical and chemical properties that enable charged toner particles to effectively and controllably adhere electrostatically to the donor roll, and to be effectively donated to a photoconductive member to form an images.
This invention separately provides rolls having coatings with tunable electrical properties.
This invention separately provides rolls having an outer surface with a highly smooth finish.
This invention separately provides rolls having a coating with improved machining characteristics.
This invention separately provides rolls that have a wear resistant outer surface.
This invention separately provides methods of making such rolls.
Exemplary embodiments of the rolls according to this invention comprise a core and an outer coating formed over the core. In some embodiments, the outer coating consists essentially of stabilized zirconia. The outer coating can provide a smooth finish and controlled electrical properties. These and other properties of the outer coating make the rolls highly suitable for use in electrostatographic imaging apparatus.
The outer coatings of the rolls can be finished to the desired finish in reduced cycle times as compared to known coating materials such as alumina and aluminatitania blends.
Other exemplary embodiments of the rolls according to this invention comprise a core and an outer coating comprising a blend of stabilized zirconia and titania formed over the core. The addition of titania to zirconia increases the conductivity of the outer coating. The amount of titania in the coating can be varied to achieve the desired electrical properties.
Exemplary embodiments of the methods of forming the rolls according to this invention comprise applying a stabilized zirconia-containing outer coating over a core. The outer coating can be applied by any suitable coating process.